Mind Over Body

Few tasks in science are so daunting as attempts to unravel the workings
of the human mind; the range of mental processes seems almost without
limit. Neurobiologists have therefore often sought clues about normal
functioning by observing the specific changes that result from brain
damage. One of the most striking of these mental disabilities is
anosognosia--derived from the Greek for "loss of knowledge"--which
was first described by French neurologist M.J.
Babinski in 1914. Anosognosia has long fascinated cognitive scientists
because it suggests that perception and self-awareness may be distinct
functions carried out by separate parts of the brain.

Anosognosia usually occurs among people who have suffered a stroke
in the right hemisphere of their brains that has made them unable to use
their left arms or legs. Such persons are said to be hemiplegic. A small
proportion of these hemiplegics display a remarkable symptom: they cannot
perceive that they are paralyzed. They insist that their paralyzed limbs
are functioning normally, even immediately after failing to perform some
simple task that requires their use.

Now two researchers at the University of
California at San Diego's Center for Research on Brain and Cognition
have shown that in some patients the effects of anosognosia are more
profound than previously recognized. Some anosognosics not only are
unaware of their own paralysis, they are also unable to perceive paralysis
in others. This finding seems to indicate that our awareness of ourselves
is inextricably entwined with our awareness of others.

The experiment, described in the August 8 issue of Nature by Vilayanur S. Ramachandran and Diane
C. Rogers-Ramachandran, a husband-and-wife team, involved three women,
two 77 years old and one 78 years old. All were paralyzed on their left
sides and hence confined to wheelchairs, as a result of strokes.

Ramachandran claims that the women were all mentally lucid, able to converse fluently and to perform simple arithmetic operations. The
researchers asked them a series of questions to test the nature of their
anosognosia: Can you walk? Can you use both hands? Can you use your right
hand? Can you use your left hand? Are both hands equally strong? The three
women answered all these questions affirmatively, even when they were
sitting in front of a mirror that belied their answers.

The U.C.S.D. scientists then asked the women to observe another person
exhibiting left hemiplegia. (In one case, the researchers presented a
healthy male student who pretended to be paralyzed.) The investigators
first established that this person, whom they called the "stooge," was
unable to respond to commands to move his left arm. They then asked the
original subjects whether the stooge was moving his arm properly or was
paralyzed.

One woman, seemingly surprised at the question, answered that "of course
he is paralyzed; he is not moving his arm." The other two women, however,
answered without hesitation that the man was "OK" and was "moving his arm
up and down." The awareness of anosognosic patients, Ramachandran
comments, "is completely warped to accommodate the strange new sensory
world they inhabit."

Previous workers have proposed that each individual's brain has a specific
neural region that contains a schema, or representation, of the
individual's body. According to this model, anosognosia occurs when brain
damage prevents new sensory data from being integrated into the schema.
The schema hypothesis might also explain the "phantom limb" phenomena that
often occur after spinal injury or amputation, which involve tactile
rather than visual hallucinations about the body.

The Ramachandrans speculate that this same region of the brain may contain
representations of other persons' bodies as well. (The fact that one of
patients perceived the stooge's paralysis correctly suggests, however,
that the regions do not completely overlap.) Experiments on monkeys,
described two years ago in Science
(Michael S. A. Graziano et al., Vol. 266, pages 1054-1057; November 11,
1994), support this hypothesis. The researchers discovered that the neural
cells in the monkeys' frontal lobes that fire when the animals perform
certain functions also show activity when they watch other monkeys perform
the same function. This work suggests a new twist on the old mind-body problem;
our bodies are, in a sense, self-projected constructs, an integral part of
our minds.

Ramachandran is designing new experiments to test whether anosognosia can
be overcome by other mental functions. In one preliminary result, he found
that an anosognosic patient would acknowledge her paralysis if he injected
her left arm with an inert saline solution but told her it was a
paralyzing anesthetic. Studying such syndromes, Ramachandran explains, can
yield insights into ancient questions about how we obtain knowledge of the
world and represent it in our brains. "We call this field 'experimental
epistemology,' just to annoy the philosophers," he says.

ABOUT THE AUTHOR(S)

John Horgan

John Horgan directs the Center for Science Writings at the Stevens Institute of Technology. His books include The End of Science and The End of War.

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